Bioequivalence and Bioavailability Forum

Dear Martin, dear Helmut!

❝ We recently encountered an unexpected behavior (at least I was not aware of it) with Fieller confidence intervals. It seems that the power for showing equivalence is not maximized at delta = 1 for rather large variances. Is there an error in the code or is this behavior well known?

This behaviour is not unexpected. See the various power curves in:

Hauschke, Steinijans, Pigeot
"Bioequivalence Studies in Drug Development"
Wiley, Chichester (2007)
Chapter 10: Equivalence assessment for clinical endpoints /
10.3 Power and sample size calculation

They all show maximum power apart from ratio 1.

This has only partly to do with the fact that we use the 'unsymmetrical' acceptance ranges [theta1=0.8, theta2=1/theta1=1.25] ('unsymmetrical' in the original domain):

library(PowerTOST)
power.RatioF(alpha=0.05, theta1=0.8, theta2=1.2, theta0=0.98, CV=0.25, n=20, design="parallel")
theta0   power
0.98    0.123749
1       0.130499
1.01    0.132072
1.02    0.1328319
1.03    0.1321316
1.04    0.1310061